The relationship between morphological and metabolic events in axotomized neurons will be explored. It is proposed to describe in detail, using light and electron microscopy, the morphological changes in the axotomized goldfish retinal ganglion cell bodies, in the regenerating axon, and during re-establishment of the tectal synapses. The metabolic correlates of the morphological changes will be investigated by injection of labelled precursors and tracing the incorporated label using radioautographic and liquid scintillation counting methods. It will therefore be possible to study changes in both synthesis and axonal transport of materials during regeneration. Radioautography as a tracing method will permit the study of the formation of new synapses by the regenerating axon. Comparisons will be made using these methods with the response of other neuronal cell types to axotomy in an attempt to describe the cellular and metabolic basis of failure of regeneration in some neurons, particularly mamalian CNS neurons. Comparisons will also be made between neurons which are forming new axonal processes by regeneration after axotomy and uninjured neurons which are forming new processes by axonal sprouting.